1. Field of the Invention
The invention concerns a method as well as a device for the burning of an artificial carbon body, especially of an anode for the aluminum fusion electrolysis, whereby a pre-formed green casting [briquette] is heated up by means of electrical resistance heating.
2. The Prior Art
The prior art includes several known methods for burning artificial carbon bodies. A distinction is made between artificial carbon bodies upon which no extreme requirements are placed with respect to a possible low electric resistance coefficient. These are customarily subjected to a burning process with a maximum of 1350.degree. C., designated in this area of the art often as "carbonization". The invention concerns this category.
Artificial carbon bodies which must in addition display extremely low resistance coefficients and/or high strength factors are produced according to the so-called Acheson method, whereby these electrodes following the carbonization are burnt by means of direct electric resistance heating at temperatures around 2800.degree. C. This process is customarily designated in this area of the art as "graphitization".
For the burning of artificial carbon bodies, for example, the following different methods are used:
1. The castings, so-called "green" castings, are placed in a gas-fired furnace and are heated extremely slowly up to temperatures between 750.degree. and 1350.degree. C. They are kept for a period of time at said temperature and then are slowly cooled. This method which is designated in this area of the art as "roasting" or "baking" lasts between 15 and 50 days.
2. Graphitization of "roasted", that is preburned, artificial carbon bodies according to the Acheson method by means of electric resistance heating in a furnace, wherein the carbon castings themselves are employed as heating elements. Depending upon the size of the form bodies to be produced, the graphitization process takes between several hours to several days.
3. Burning of larger artificial carbon form bodies, for example, for the use in atomic energy reactors, by means of direct resistance heating of the green castings with simultaneous application of high pressures, for example, in the order of magnitude of 150 to 350 bar and above, in a stable mold under a mechanical power press, whereby relatively high heating rates come into use. For example, in the Great Britain Pat. No. 794,989, page 8, lines 52 through 54, heating rates are cited between 2.degree. and 1000.degree. C./min. The actual heating rates are in these instances dependent upon the dimensions of the body which is being heated.
A disadvantage in the use of the so-called "roasting" in gas-heated furnaces is that a duration of up to 50 days leads to uneconomical furnace dimensions and heat losses and thus correspondingly high costs of manufacture. This method is reliable though uneconomical.
The method of electric resistance heating in a mold under high pressures requires the employment of extremely expensive mechanical power press devices as well as pressure-proof forms, and it is thus not acceptable for economic reasons because of the outlay for machines and costs, for example, for the production of large burned carbon anodes for the aluminum fusion electrolysis.
There is thus a need for an economical procedure for the manufacture of large burned artificial carbon bodies, especially those usable as anodes for aluminum fusion electrolysis, with individual piece weights between 500 and 5000 kg. In such a method, preformed green blocks are burned with as high a heating rate as possible by means of electric resistance heating without the use of externally applied pressure.